// Iterative C program to compute modular power
#include <stdio.h>

/* Iterative Function to calculate (x^y)%p in O(log y) */
int power(int x, unsigned int y, int p)
{
    int res = 1;     // Initialize result

    x = x % p; // Update x if it is more than or
                // equal to p

    while (y > 0)
    {
        // If y is odd, multiply x with result
        if (y & 1)
            res = (res*x) % p;

        // y must be even now
        y = y>>1; // y = y/2
        x = (x*x) % p;
    }
    return res;
}

// Driver program to test above functions
int main()
{
int x = 2;
int y = 5;
int p = 13;
printf("Power is %u", power(x, y, p));
return 0;
}