630F - Selection of Personnel - CodeForces Solution

#include <bits/stdc++.h>
using namespace std;
#define fastio  ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL);

#define prnt(x) for(auto &it: x)cout<<it<<" ";cout<<"\n";
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())

typedef long long ll;
typedef vector<ll> vll;
const ll N = 780, inf=2e18;
ll mod = 1000000007;
ll func(ll n, ll r){
    ll ans=1;
    for(ll i=0; i<r; i++){
        ans*=(n-i);
        ans/=(i+1);
    }
    return ans;
}
void solve(ll tc)
{
    ll n;
    cin>>n;
    ll ans=0;
    for(ll i=5; i<=7; i++){
        ans+=func(n, i);
    }
    cout<<ans<<endl;
}
int main()
{
    fastio;ll T = 1;
    //cin >> T;
    for (ll i = 1; i <= T; i++)solve(i);
    return 0;
}