#include<cstdio>
int a[1000]={1,3,6,10,15,21,28,36,45,55,66,78,91,105,120,136,153,171,190,210,231,253,276,300,325,351,378,406,435,465,496,528,561,595,630,666,703,741,780,820,861,903,946,990,1035,1081,1128,1176,1225,1275,1326,1378,1431,1485,1540,1596,1653,1711,1770,1830,1891,1953,2016,2080,2145,2211,2278,2346,2415,2485,2556,2628,2701,2775,2850,2926,3003,3081,3160,3240,3321,3403,3486,3570,3655,3741,3828,3916,4005,4095,4186,4278,4371,4465,4560,4656,4753,4851,4950,5050,5151,5253,5356,5460,5565,5671,5778,5886,5995,6105,6216,6328,6441,6555,6670,6786,6903,7021,7140,7260,7381,7503,7626,7750,7875,8001,8128,8256,8385,8515,8646,8778,8911,9045,9180,9316,9453,9591,9730,9870,10011,10153,10296,10440,10585,10731,10878,11026,11175,11325,11476,11628,11781,11935,12090,12246,12403,12561,12720,12880,13041,13203,13366,13530,13695,13861,14028,14196,14365,14535,14706,14878,15051,15225,15400,15576,15753,15931,16110,16290,16471,16653,16836,17020,17205,17391,17578,17766,17955,18145,18336,18528,18721,18915,19110,19306,19503,19701,19900,20100,20301,20503,20706,20910,21115,21321,21528,21736,21945,22155,22366,22578,22791,23005,23220,23436,23653,23871,24090,24310,24531,24753,24976,25200,25425,25651,25878,26106,26335,26565,26796,27028,27261,27495,27730,27966,28203,28441,28680,28920,29161,29403,29646,29890,30135,30381,30628,30876,31125,31375,31626,31878,32131,32385,32640,32896,33153,33411,33670,33930,34191,34453,34716,34980,35245,35511,35778,36046,36315,36585,36856,37128,37401,37675,37950,38226,38503,38781,39060,39340,39621,39903,40186,40470,40755,41041,41328,41616,41905,42195,42486,42778,43071,43365,43660,43956,44253,44551,44850,45150,45451,45753,46056,46360,46665,46971,47278,47586,47895,48205,48516,48828,49141,49455,49770,50086,50403,50721,51040,51360,51681,52003,52326,52650,52975,53301,53628,53956,54285,54615,54946,55278,55611,55945,56280,56616,56953,57291,57630,57970,58311,58653,58996,59340,59685,60031,60378,60726,61075,61425,61776,62128,62481,62835,63190,63546,63903,64261,64620,64980,65341,65703,66066,66430,66795,67161,67528,67896,68265,68635,69006,69378,69751,70125,70500,70876,71253,71631,72010,72390,72771,73153,73536,73920,74305,74691,75078,75466,75855,76245,76636,77028,77421,77815,78210,78606,79003,79401,79800,80200,80601,81003,81406,81810,82215,82621,83028,83436,83845,84255,84666,85078,85491,85905,86320,86736,87153,87571,87990,88410,88831,89253,89676,90100,90525,90951,91378,91806,92235,92665,93096,93528,93961,94395,94830,95266,95703,96141,96580,97020,97461,97903,98346,98790,99235,99681,100128,100576,101025,101475,101926,102378,102831,103285,103740,104196,104653,105111,105570,106030,106491,106953,107416,107880,108345,108811,109278,109746,110215,110685,111156,111628,112101,112575,113050,113526,114003,114481,114960,115440,115921,116403,116886,117370,117855,118341,118828,119316,119805,120295,120786,121278,121771,122265,122760,123256,123753,124251,124750,125250,125751,126253,126756,127260,127765,128271,128778,129286,129795,130305,130816,131328,131841,132355,132870,133386,133903,134421,134940,135460,135981,136503,137026,137550,138075,138601,139128,139656,140185,140715,141246,141778,142311,142845,143380,143916,144453,144991,145530,146070,146611,147153,147696,148240,148785,149331,149878,150426,150975,151525,152076,152628,153181,153735,154290,154846,155403,155961,156520,157080,157641,158203,158766,159330,159895,160461,161028,161596,162165,162735,163306,163878,164451,165025,165600,166176,166753,167331,167910,168490,169071,169653,170236,170820,171405,171991,172578,173166,173755,174345,174936,175528,176121,176715,177310,177906,178503,179101,179700,180300,180901,181503,182106,182710,183315,183921,184528,185136,185745,186355,186966,187578,188191,188805,189420,190036,190653,191271,191890,192510,193131,193753,194376,195000,195625,196251,196878,197506,198135,198765,199396,200028,200661,201295,201930,202566,203203,203841,204480,205120,205761,206403,207046,207690,208335,208981,209628,210276,210925,211575,212226,212878,213531,214185,214840,215496,216153,216811,217470,218130,218791,219453,220116,220780,221445,222111,222778,223446,224115,224785,225456,226128,226801,227475,228150,228826,229503,230181,230860,231540,232221,232903,233586,234270,234955,235641,236328,237016,237705,238395,239086,239778,240471,241165,241860,242556,243253,243951,244650,245350,246051,246753,247456,248160,248865,249571,250278,250986,251695,252405,253116,253828,254541,255255,255970,256686,257403,258121,258840,259560,260281,261003,261726,262450,263175,263901,264628,265356,266085,266815,267546,268278,269011,269745,270480,271216,271953,272691,273430,274170,274911,275653,276396,277140,277885,278631,279378,280126,280875,281625,282376,283128,283881,284635,285390,286146,286903,287661,288420,289180,289941,290703,291466,292230,292995,293761,294528,295296,296065,296835,297606,298378,299151,299925,300700,301476,302253,303031,303810,304590,305371,306153,306936,307720,308505,309291,310078,310866,311655,312445,313236,314028,314821,315615,316410,317206,318003,318801,319600,320400,321201,322003,322806,323610,324415,325221,326028,326836,327645,328455,329266,330078,330891,331705,332520,333336,334153,334971,335790,336610,337431,338253,339076,339900,340725,341551,342378,343206,344035,344865,345696,346528,347361,348195,349030,349866,350703,351541,352380,353220,354061,354903,355746,356590,357435,358281,359128,359976,360825,361675,362526,363378,364231,365085,365940,366796,367653,368511,369370,370230,371091,371953,372816,373680,374545,375411,376278,377146,378015,378885,379756,380628,381501,382375,383250,384126,385003,385881,386760,387640,388521,389403,390286,391170,392055,392941,393828,394716,395605,396495,397386,398278,399171,400065,400960,401856,402753,403651,404550,405450,406351,407253,408156,409060,409965,410871,411778,412686,413595,414505,415416,416328,417241,418155,419070,419986,420903,421821,422740,423660,424581,425503,426426,427350,428275,429201,430128,431056,431985,432915,433846,434778,435711,436645,437580,438516,439453,440391,441330,442270,443211,444153,445096,446040,446985,447931,448878,449826,450775,451725,452676,453628,454581,455535,456490,457446,458403,459361,460320,461280,462241,463203,464166,465130,466095,467061,468028,468996,469965,470935,471906,472878,473851,474825,475800,476776,477753,478731,479710,480690,481671,482653,483636,484620,485605,486591,487578,488566,489555,490545,491536,492528,493521,494515,495510,496506,497503,498501,499500};
int main()
{
    int n,m;
    scanf("%d %d",&n,&m);
    int x=m-n;
    printf("%d",a[x-1]-m);
    return 0;
}

Measured memory_bytes: 128