#include <math.h>
#include <stdio.h>

int main()
{
    int n;
    printf("Nhap n :");
    scanf("%d",&n);
    float S=0;
    int i=1;
    while(i<=n)
    {
        S=S+1.0/(i*(i+1));
        i++;
    }
    printf("S=%f",S);
    return 0;
}