#include <stdio.h>
int main(){
int N;
double f=2.0;
double m=1.0;
int i;
double c;
double my_sum=0.0;
if (scanf("%d",&N)!=0){
for (i=1;i<=N;i++){
my_sum+=f/m;
c = f;
f = f+m;
m = c;
}
printf("%.2f",my_sum);
}else{
printf("输入信息出错");
}
return 0;
}
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