/******************************************************************************
 
Welcome to GDB Online.
GDB online is an online compiler and debugger tool for C/C++.
Code, Compile, Run and Debug online from anywhere in world.
 
*******************************************************************************/
#include <iostream>
using namespace std;
int main()
{ int n,s;
cin>>n;
for(int i=1;i<=n;i++)
  s=s+i;
cout<<s;  
 
 
 
 
	return 0;
}
 
 
 

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7