#include<stdio.h>
int main(){
    int i,n;
    scanf("%d",&n);
    float sum=0.0;
    float a=1;
    float b=2;
    for(i=1;i<=n;i++){
        sum=sum+1.0*b/a;
        int c=a;
        a=b;
        b=c+b;
    }
    printf("s=%.2f\n", sum);
    return 0;
}

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