task3.c

#include<stdio.h>
int main(){
    int n ;
printf("n=");
    scanf_s("%lld", &n);
    int sum = 0, i = 0, t = 1;
    
    while (i <= n) {
        sum += t;
        t *= 2;
        i++;
    }
    printf("sum=%lld\n", sum);
}