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#include <stdio.h>
double a[505];
int main(void){
    a[0]=1;
    a[1]=2;
    double sum=3;
    for(int i=2;i<=500;i++){
        a[i]=sum*2/i;
        sum+=a[i];
    }
    int n;
    while(scanf("%d",&n)==1){
        printf("%.6f\n",a[n]);
    }
    return 0;
}
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