#include<iostream> using namespace std; int main() { /* int n,s=1,i; cin>>n; for(i=0;i<n-1;i++){ s+=i; } cout<<s; */ /* int n,s=10000,i,j; cin>>n; if(n%2==1){ cout<<s-(n/2)*1; }else{ cout<<s-(n/2-1)*2; } */ /* int m,n,i=0,j=0; cin>>n>>m; for(int a=n;a<=m;a++){ if(a%2==0){ i=i+a; }else{ j=j+a; } } cout<<i<<' '<<j; */ int sun=0,j; cin>>j; for(int i=1;i<=j;i++){ sun+=i; } cout<<sun; return 0; }