7-35 猴子吃桃问题

#include<stdio.h>
int main(){
    int N;
    int X1=0;
    int X2=1;
    scanf("%d",&N);
    N--;
    while(N>0){
        X1 = (X2 + 1) * 2;
        X2 = X1;
        N--;
    }
    printf("%d",X1);
    return 0;
}