#include<stdio.h>
#include<stdlib.h>
#include <math.h>
#define N 100

void swap(double a[N], int n) {
    int i =0;
    for (i = 0; i + 1 < n; i += 2) {
        double tmp = a[i];
        a[i] = a[i + 1];
        a[i + 1] = tmp;
    }
}

int main(){
    double a[N];
    int n, i;
    printf("Input the size of the massiv: ");
    scanf("%d", &n);
    for (i = 0; i < n; i++) {
        printf("a[%d] = ", i);
        scanf("%lg", &a[i]);
    }
    swap(a, n);

    for (i = 0; i < n; i++){
        printf("%lg", a[i]);
    }

    system("pause");
    return 0;
}