C :

#include <stdio.h>
#include <math.h>
#include <string.h>

double fact(int m)
{
	int j;
	double s=1;
	for (j=1;j<=m;j++)
		s*=j;
	return s;
}

int main()
{
	int i,n;
	double s,sum=0;
	scanf ("%d",&n);
	for (i=1;i<=n;i++)
	{
		s=1.0/fact(i);
		sum+=s;
	}
	printf ("sum=%.5lf\n",sum);
	return 0;
}

C++ :

#include<iostream>
 
using namespace std;
 
double fact(int k);
int main() {
    int n;
    double sum = 0;
    cin >> n;
     
    for (int i = 1; i <= n; i++) {
        if (fact(i) < 10000000)
            sum = sum + 1 / fact(i);
        else
            break;
    }
    cout.precision(6);
    cout.setf(ios_base::showpoint);
    cout << "sum=" << sum;
 
    return 0;
}
double fact(int k) {
    int sum = 1;
    for (int i = 1; i<= k; i++)
        sum = sum * i;
    return sum;
}