C :

#include <stdio.h>

long long int f[50];

int main()

{
    f[1] = 0;
    f[2] = 1;
    f[3] = 2;
    for(int i = 4;i <= 50;++i)
        f[i] = f[i - 1] + f[i - 2];
    int m;
    while(~scanf("%d",&m))
    {
        printf("%lld\n",f[m]);
    }
    return 0;
}

C++ :

#include <stdio.h>

long long int f[50];

int main()

{
    f[1] = 0;
    f[2] = 1;
    f[3] = 2;
    for(int i = 4;i <= 50;++i)
        f[i] = f[i - 1] + f[i - 2];
    int m;
    while(~scanf("%d",&m))
    {
        printf("%lld\n",f[m]);
    }
    return 0;
}