Buggy python submission (verdict: Runtime Error):
import bisect
import math
N,D,A=map(int,input().split())
monster=[list(map(int,input().split())) for i in range(N)]
monster.sort(key=lambda x:x[0])
minus=[0]*N
ans=0
damage=0
for i in range(N):
    monster[i][1]-=damage
    if(monster[i][1]<=0):
        continue
    cnt=math.ceil(monster[i][1]/A)
    ans+=cnt
    if(D==0):
        continue
    b=bisect.bisect_left(monster[0],monster[i][0]+2*D)
    damage+=A*cnt
    damage-=minus[i]
    if(b!=0):
        minus[b-1]+=cnt*A
print(ans)

Fixed submission:
import bisect
import math
N,D,A=map(int,input().split())
tmp=[list(map(int,input().split())) for i in range(N)]
tmp.sort(key=lambda x:x[0])
monster=[];X=[]
for i in range(N):
    monster.append(tmp[i][1]);X.append(tmp[i][0])
minus=[0]*(N+1)
ans=0
damage=0
for i in range(N):
    damage-=minus[i]
    monster[i]=max(0,monster[i]-damage)
    if(monster[i]==0):
        continue
    cnt=math.ceil(monster[i]/A)
    monster[i]=0
    ans+=cnt
    b=bisect.bisect_left(X,X[i]+2*D+1)
    minus[b]+=cnt*A
    damage+=A*cnt
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import math
import sys
input=sys.stdin.buffer.readline
def main():
    N,D,A=map(int,input().split())
    monster=[list(map(int,input().split())) for i in range(N)]
    monster.sort(key=lambda x:x[0])
    ans=0
    for i in range(N):
        if(monster[i][1]==0):
            continue
        cnt=math.ceil(monster[i][1]/A)
        ans+=cnt
        for j in range(i+1,N):
            if monster[j][0]-monster[i][0]>2*D:
                break
            monster[j][1]=max(0,monster[j][1]-cnt*A)
    print(ans)

if __name__=='__main__':
    main()

Fixed submission:
import bisect
import math
N,D,A=map(int,input().split())
tmp=[list(map(int,input().split())) for i in range(N)]
tmp.sort(key=lambda x:x[0])
monster=[];X=[]
for i in range(N):
    monster.append(tmp[i][1]);X.append(tmp[i][0])
minus=[0]*(N+1)
ans=0
damage=0
for i in range(N):
    damage-=minus[i]
    monster[i]=max(0,monster[i]-damage)
    if(monster[i]==0):
        continue
    cnt=math.ceil(monster[i]/A)
    monster[i]=0
    ans+=cnt
    b=bisect.bisect_left(X,X[i]+2*D+1)
    minus[b]+=cnt*A
    damage+=A*cnt
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import math
N,D,A=map(int,input().split())
monster=[list(map(int,input().split())) for i in range(N)]
monster.sort(key=lambda x:x[0])
ans=0
for i in range(N):
    if(monster[i][1]==0):
        continue
    cnt=math.ceil(monster[i][1]/A)
    ans+=cnt
    for j in range(i+1,N):
        if monster[j][0]-monster[i][0]>2*D:
            break
        monster[j][1]=max(0,monster[j][1]-cnt*A)
print(ans)

Fixed submission:
import bisect
import math
N,D,A=map(int,input().split())
tmp=[list(map(int,input().split())) for i in range(N)]
tmp.sort(key=lambda x:x[0])
monster=[];X=[]
for i in range(N):
    monster.append(tmp[i][1]);X.append(tmp[i][0])
minus=[0]*(N+1)
ans=0
damage=0
for i in range(N):
    damage-=minus[i]
    monster[i]=max(0,monster[i]-damage)
    if(monster[i]==0):
        continue
    cnt=math.ceil(monster[i]/A)
    monster[i]=0
    ans+=cnt
    b=bisect.bisect_left(X,X[i]+2*D+1)
    minus[b]+=cnt*A
    damage+=A*cnt
print(ans)