#include <bits/stdc++.h>
#define ll long long int
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time__(d) \
    for ( \
        auto blockTime = make_pair(chrono::high_resolution_clock::now(), true); \
        blockTime.second; \
        debug("%s: %d ms\n", d, (int)chrono::duration_cast<chrono::milliseconds>(chrono::high_resolution_clock::now() - blockTime.first).count()), blockTime.second = false \
    )
using namespace std;
 
ll sum_till_a(int a){
    ll res=0;
    while(a){
        res+=a;
        a--;
    }
    return res;
}
 
int main(){
    ll a , res=0;
    cin>>a;
 
    time__("Solve Time"){
        res = sum_till_a(a);
    }
 
    cout<<res;
    return 0;
}

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

OTk5OTk5OTk=

99999999