Compute pi

#include <stdio.h>

    double compute_pi(int N){
        double i=2,j=1;

        int cont=0;

        double mult = 1;

        while(cont<N){

            mult = mult * (i/j);

            if(cont%2==0) j = j + 2;
                else i = i + 2;



            cont++;
        }

    return mult*2;

    }

int main(){
    int N;

    double pi;

    scanf("%d", &N);

    pi = compute_pi(N);

    printf("%.12lf", pi);

    return 0;

}