#include<cstdio>

int main(){
    int n=101;
    int arr[105];
    int sum = 0;
    for(int i=1;i<101;i++){
        arr[i]=sum+=i;
    }
    while(scanf("%d",&n)!=EOF){
        printf("%d\n",arr[n]);
    }
    return 0;
}
