#include <vector>
#include <algorithm>
#include <stdio.h>
int main(int argc, char**argv)
{
    std::vector<int> list;
    int n= argc<2 ? 100 : strtol(argv[1],0,0);
    for (int i=1 ; i<n ; i++)
        list.push_back(i);

    int sum=0;
    std::for_each(list.begin(), list.end(), [&sum](int x) { sum+=x; });
    printf("sum=%d\n", sum);

    return 0;
}