#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

int descending_compare(const void *a, const void *b){
    if (*(long long*)a > *(long long*)b){
        return -1;
    }else if (*(long long*)a == *(long long*)b){
        return 0;
    }else{
        return 1;
    }
}

int ascending_compare(const void *a, const void *b){
    if (*(int*)a < *(int*)b){
        return -1;
    }else if (*(int*)a == *(int*)b){
        return 0;
    }else{
        return 1;
    }
}


int lower_bound(int *a, int n, int key){
    int left, mid, right;
    left = 0, right = n;
    mid = (left + right)/2;
    while ((left+1 != mid || mid+1 != right) && mid != left){
        if (key > a[mid]){
            left = mid;
        }else{
            right = mid+1;
        }
        mid = (left + right)/2;
    }
    if (a[left] >= key)return left;
    if (a[mid] >= key)return mid;
    if (a[right] >= key)return right;
    return n;
}

//greatest common divisor
unsigned long gcd(unsigned long x, unsigned long y){
    if (y == 0){ 
        return x;
    }else if (x > y){
        return gcd(y, x % y);
    }else{
        return gcd(x, y % x);
    }
}

unsigned long lcm(unsigned long x, unsigned long y){
    unsigned long g = gcd(x, y);
    return x*y/g;

}



long long factorial(int x){
    long long rtn = 1;
    int i;
    for (i = x; i > 1; i--){
        rtn = (rtn*i);
    }
    return rtn;
}

/*
int struct_ascending_compare(const void *p, const void *q) {
return ((struct_name*)p)->member_name - ((struct_name*)q)->member_name;
}*/

/*unsigned long long pascal[100][100] = {0};
void make_pascal(void){
    for (int i = 0; i < 100; i++){
        pascal[i][0] = 1;
    }
    pascal[1][1] = 1;
    for (int i = 2; i < 100; i++){
        for (int j = 1; j < 100; j++){
           pascal[i][j] = (pascal[i-1][j-1]+pascal[i-1][j]);
        }
    }
}*/
int head[1005];
int next[2005];
int to[2005];
int weight[2005];
long long v[1005];
int vb[1005] = {0};
int n, m;
long long ans;

int dfs(int crt){
    int edge = head[crt];
    while (edge != -1){
        if (vb[to[edge]] != 1 && v[to[edge]] < v[crt] + weight[edge]){
            v[to[edge]] = v[crt] + weight[edge];
            vb[to[edge]] = 1;
            dfs(to[edge]);
        }
        edge = next[edge];  
    }
    vb[crt] = 0;
    return 0;
}

int dfs2(int crt){
    int edge = head[crt];
    if (v[n] > ans) return 0;
    while (edge != -1){
        if (vb[to[edge]] != 3 && v[to[edge]] <= v[crt] + weight[edge]){
            if (v[to[edge]] < v[crt] + weight[edge]){
                v[to[edge]] = v[crt] + weight[edge];
            }
            vb[to[edge]]++;
            dfs2(to[edge]);
        }
        edge = next[edge];  
    }
    vb[crt]--;
    return 0;
}


int main2(void){
    for (int i = 0; i < 1005; i++){
        head[i] = -1;
        v[i] = -1000000000000000;
    }
    scanf("%d %d", &n, &m);
    int a, b, c;
    for (int i = 0; i < m; i++){
        scanf("%d %d %d", &a, &b, &c);
        next[i] = head[a];
        head[a] = i;
        to[i] = b;
        weight[i] = c;
    }
    v[1] = 0;
    vb[1] = 1;
    dfs(1);
    ans = v[n];
    for (int i = 0; i < 1005; i++){
        vb[i] = 0;
    }
    v[1] = 0;
    vb[1] = 1;
    dfs2(1);
    if (ans >= v[n]){
        printf("%lld\n", ans);
    }else{
        printf("inf\n");
    }
    return 0;
}

int main(void){
    int n;
    scanf("%d", &n);
    printf("%d\n", (n+1)*n/2);
}

Measured memory_bytes: 128