#include <stdio.h> int main() { int n,sum; scanf("%d",&n); sum=nsum(n); printf("%d\n",sum); return 0; } int nsum(int n) { int i,sum=0; for(i=1;i<=n;i++) { sum+=i; } return sum; }

here n=5
so the sum of numbers from 1 to 5 is 15